High gas velocity start-up of an ethylene cracking furnace

Abstract

In chemical processes for cracking hydrocarbons, reactors are subject to coking During the decoke process carburization of the metal substrate can occur, negatively impacting reactor life. Decokes are also costly due to down-time where costs are incurred without production of commercial products. Reducing the frequency of decokes provides an opportunity to reduce the financial impacts of downtimes. A start-up procedure is described herein that limits initial coke deposition, leading to a reduced tendency for carburization of the metal substrate, improving reactor life, and more importantly, extending reactor run length.

1 . A procedure for starting up a hydrocarbon cracking furnace, wherein the hydrocarbon cracking furnace comprises a furnace tube, and the furnace tube comprises an inlet, an outlet, and a point of incipient cracking between the inlet and the outlet, wherein the procedure comprises:
 introducing a fluid comprising a hydrocarbon and steam to the inlet;   maintaining a temperature of the fluid at the inlet at 25° C. to 225° C.; and   controlling a fluid velocity at the point of incipient cracking to 90 m/s to 115 m/s for at least 24 hours by varying a flow rate of the fluid at the inlet, by varying a fluid property of the fluid at the inlet, or both.   
     
     
         2 . The procedure of  claim 1 , wherein the fluid velocity is controlled to 90 m/s to 110 m/s. 
     
     
         3 . (canceled) 
     
     
         4 . The procedure of  claim 1 , wherein the fluid velocity is controlled for at least 5 days. 
     
     
         5 . The procedure according to  claim 1 , wherein the fluid velocity is controlled for at least 10 days. 
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . The procedure of  claim 1 , wherein the hydrocarbon comprises one or more C1-C4 alkanes. 
     
     
         9 . The procedure of  claim 1 , wherein the fluid velocity is calculated using the Ideal Gas Law, based on an average of a number-average molecular weight of the fluid proximate the inlet and a number-average molecular weight of the fluid proximate the outlet. 
     
     
         10 . The procedure of  claim 1 , wherein the fluid velocity is controlled within 3 hours of the introduction of the fluid. 
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . The procedure of  claim 1 , wherein the temperature of the fluid at the inlet is maintained at 90° C. to 160° C. 
     
     
         14 . The procedure of  claim 1 , wherein a number average molecular weight of the fluid at the inlet is 16 g/mol to 60 g/mol. 
     
     
         15 . (canceled) 
     
     
         16 . The procedure of  claim 1 , wherein a pressure drop of the fluid from the inlet to the outlet is 275 kPa to 400 kPa. 
     
     
         17 . The procedure of  claim 1 , further comprising controlling a fluid velocity at the outlet to 190 m/s to 250 m/s. 
     
     
         18 . (canceled) 
     
     
         19 . The procedure of  claim 1 , further comprising controlling a fluid velocity at the outlet to 180 m/s to 260 m/s for at least 48 hours. 
     
     
         20 . (canceled) 
     
     
         21 . The procedure of  claim 1 , hydrocarbon comprises a mixture of a fresh hydrocarbon and a recycled hydrocarbon. 
     
     
         22 . The procedure of  claim 8 , wherein the C1-C4 alkane comprises ethane. 
     
     
         23 . The procedure of  claim 1 , wherein the hydrocarbon comprises naphtha, heavy aromatic distillate, aromatic hydrocarbons, or any mixture thereof. 
     
     
         24 . The procedure of  claim 1 , wherein the fluid velocity is controlled for an entire duration of a run length of the hydrocarbon cracking furnace. 
     
     
         25 . (canceled) 
     
     
         26 . (canceled) 
     
     
         27 . (canceled) 
     
     
         28 . (canceled) 
     
     
         29 . The procedure of  claim 4 , wherein a run length of operating the hydrocarbon cracking furnace after the starting-up procedure is extended by at least 15% as compared to the same procedure that does not include controlling the fluid velocity at the point of incipient cracking. 
     
     
         30 . The procedure of  claim 29 , wherein the run length is extended by at least 30%. 
     
     
         31 . The procedure of  claim 1 , wherein a run length of operating the hydrocarbon cracking furnace after the starting-up procedure is extended by at least 8 days as compared to the same procedure that does not include controlling the fluid velocity at the point of incipient cracking. 
     
     
         32 . The procedure of  claim 31 , wherein the run length is extended by at least 16 days.